If the Arma 3 version is fully stocked why doesn't everyone just play it?

From what I see everyone wants Dayz to have a bunch of features that already existed in the Arma 3 mod.

I've never played Arma 3, I've just seen videos. My feed will show me videos of Dayz and Arma 3 and Arma 3 looks like what Dayz should look like in like 5 years, helicopters, etc...

So why doesn't everybody just play the Arma 3 mod? Like what's the difference really?